The present invention relates to a method of processing signals from a towed linear antenna. It notably resolves right-left ambiguity on such an antenna when it is activated, in other words when it is receiving echoes produced from emissions of an active sonar.
There are known techniques for resolving this right-left ambiguity, described in particular in the French patent no.8911749 filed by the company THOMSON-CSF on 8 Sep. 1989 and published on 15 Mar. 1991 under the U.S. Pat. No. 2,651,950 and delivered on 17 Apr. 1992, which consist in replacing each omnidirectional hydrophone by at least 3 hydrophones mounted in a plane perpendicular to the axis of the linear antenna and spread around a circle, inside the antenna and centered on its axis. In this manner, a volumic antenna is constituted enabling construction of antenna responses with right-left rejection capabilities. In particular, the processing of the signals enables a “zero” to be created in the ambiguous direction relative to the setpoint direction of the channel.
To remove the ambiguity satisfactorily using this technique, it is necessary that the “triplets” of hydrophones (or more generally the “n-multiplets”) be aligned so as to constitute a set of 3 (n) linear sub-antennas. This linearity can be assured by means of rigid links between the triplets, but this has the disadvantage of working well only for antennas that are not too long. However it is increasingly common to reduce the working frequency in order to increase the range, but this reduction generally implies increasing the length of the antennas proportionally, in which case it becomes increasingly difficult to control the linearity of the sub-antennas.
Moreover, since the antenna diameter is small compared with the wavelength, the creation of a zero leads to signal losses that become larger at lower frequencies, in particular when the dominant noise is decorrelated between hydrophones of the same triplet, which represents a second very serious disadvantage.